Types of Hybrid Cars

There are two major types of hybrid cars: full hybrids and mild hybrids. Both types have a gasoline engine, electric motor, and batteries, but they use the electric motor in different ways. These variations result in different benefits in terms of fuel economy and environmental impact.

Full hybrids are the most common type of hybrid on the market today. In full hybrids, the electric motor is fully functional—it can power the car on its own, assist the gasoline engine, recharge the batteries, and start the car. When full hybrids idle or move at slow speeds, the gasoline engine turns off and the electric motor powers the car on its own. Full hybrids also average the most fuel savings.

Full hybrids are especially beneficial for people who do a lot of city driving. Most conventional cars get better gas mileage on the highway than they do in stop-and-go city traffic: every time you step on the brake, you waste the energy produced by burning fuel. But full hybrids often get better mileage in the city, for two reasons:

Full hybrids provide gas savings of up to 60% in city driving and 20% in highway driving.

The following table lists several of the most popular models of full hybrid cars and trucks, including each hybrid’s fuel economy rating (along with comparable fuel economy for the conventional, nonhybrid version of that model, if applicable). All fuel economy ratings are reported for 2007 models with automatic transmissions and 4-cylinder engines, unless otherwise noted.

Mild hybrids are hybrid cars that don’t ever use the electric motor to power the car entirely on its own. Mild hybrids can be broken down into two further subcategories—assist hybrids and stop/start hybrids—based on how they do use their electric motors.

The first hybrid car introduced in the United States, the Honda Insight, is an assist hybrid. The electric motor in an assist hybrid doesn’t power the transmission by itself. Instead, the electric motor assists the gasoline engine to move the car. Because it is assisted by the electric motor, the gasoline engine of an assist hybrid is smaller and uses less gasoline than that of a conventional car.

Like conventional cars, assist hybrids get better highway mileage than city mileage—the Insight has the best highway fuel economy of any mass-produced car on the road today. Assist hybrids generally provide gasoline savings of a little over 20% in city driving and just under 20% in highway driving.

Assist hybrids don’t come in as many models as full hybrids. The following table lists several of the most popular models of assist hybrid cars, including each hybrid’s fuel economy rating (along with comparable fuel economy for the conventional version of that model, if applicable). All fuel economy ratings are reported for 2007 models with automatic transmissions and 4-cylinder engines, unless otherwise noted. (Note that new Honda Insights are no longer available—the final model year was 2006. The Insight will be replaced by an entirely new hybrid model in 2009.)

The electric motor in a stop/start hybrid doesn’t power the car on its own or assist the gasoline-powered engine. Instead, the motor serves as a starter for the gasoline-powered engine, turning it on and off as needed. Though a stop/start hybrid doesn’t provide gas mileage savings while the car is actually moving, it does provide savings when the car is idling. The overall fuel economy savings in stop/start hybrids isn’t huge: a stop/start hybrid generally uses 10–15% less gasoline than its conventional counterpart. However, stop/start hybrids have lower purchase prices than full and assist hybrids since they contain less of the most expensive hybrid technology.

The stop/start hybrid approach is particularly suited to heavy-duty trucks, which use a lot of fuel, making even a 10% improvement in fuel economy significant. Some stop/start hybrid trucks can also serve as generators, providing a power source into which you can plug electrical devices.

Only a few stop/start hybrids are currently on the market. The table below lists two popular models, including each hybrid’s fuel economy rating (along with comparable fuel economy for the conventional version of that model). All fuel economies are reported for 2007 models with automatic transmissions.